1. Field of the Invention
The present invention relates to a compensator and more particularly refers to a new and improved multi-layer compensator, the interspaces of which can be monitored, suitable for use in nuclear power plants.
2. Description of the Prior Art
Compensators are known components to compensate for thermal expansions in piping. Compensators constructed from several closely spaced layers which permit a certain amount of shift between them are used if the ability to expand and the life of the compensator bellows are to be increased, while the properties (for instance, the pressure strength) are to remain unchanged from single-layer compensators. If there is a medium inside the bellows, the escape of which must be prevented, monitoring the individual layers for leaks becomes increasingly important. This can be done in known manner in that between the different spaces so formed, pressure differences are maintained, and a change of pressure differences can give indications of leaks. To make it easier for the individual layers to slide on each other, they are made of sheet metal with the least possible surface roughness. It was found that the then remaining very thin gap does not permit gas transport within acceptable periods of time. It has been proposed to arrange a wire screen as a spacer between the individual layers to increase the size of the gap. However, excessive local pressure occurs, whereby notches are caused in the sheet metal pieces which can be the starting point for the later formation of leaks. The jamming of the wires in the notches furthermore inhibits the shift between the individual layers, and thereby, the ability to expand is considerably reduced. Consequently, the decisive advantage of the multi-layer compensator over the single-layer one would get is lost. Also, when testing the compensator by means of the well-known eddy current testing method, the wires running in the circumferential direction has a disturbing effect.
Additional problems arise if the compensator is to be used in high-temperature nuclear power plants, in which, for instance, helium with slight hydrogen contamination circulates at temperatures up to 950.degree. C. In particular, the danger then exists that the individual layers are joined together by friction welding and the compensator thereby loses its ability to expand.
A method familiar to those skilled in the art as "heterogeneous gaseous-phase reaction" is further known, by means of which very uniform, strongly adhering smooth oxide layers can be applied. Such oxide layers are not attacked by hydrogen and rather prevent it and its isotopes deuterium and tritium, from penetrating them.